Summary of Stock Options Outstanding (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options Outstanding, Number of Shares	6,948,456	5,789,777	4,315,098	3,255,446
Options Outstanding, weighted-average exercise price	$ 3.08	$ 3.39	$ 4.11	$ 6.09
Options exercisable, Number of Shares	4,384,643	3,472,428	2,446,730
Options exercisable, weighted-average exercise price	$ 3.83
Weighted- Average Remaining Contractual Life	6 years 10 months 24 days
$ 0.96-$ 1.32
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of Exercise Prices, Lower Limit	$ 0.96
Range of Exercise Prices, Upper Limit	$ 1.32
Options Outstanding, Number of Shares	895,756
Options Outstanding, weighted-average exercise price	$ 1.21
Options exercisable, Number of Shares	772,004
Options exercisable, weighted-average exercise price	$ 1.20
Weighted- Average Remaining Contractual Life	5 years 7 months 6 days
$ 1.33-$ 1.60
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of Exercise Prices, Lower Limit	$ 1.33
Range of Exercise Prices, Upper Limit	$ 1.6
Options Outstanding, Number of Shares	1,684,491
Options Outstanding, weighted-average exercise price	$ 1.47
Options exercisable, Number of Shares	992,728
Options exercisable, weighted-average exercise price	$ 1.48
Weighted- Average Remaining Contractual Life	7 years 9 months 18 days
$ 1.61-$ 2.00
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of Exercise Prices, Lower Limit	$ 1.61
Range of Exercise Prices, Upper Limit	$ 2
Options Outstanding, Number of Shares	1,715,544
Options Outstanding, weighted-average exercise price	$ 1.72
Options exercisable, Number of Shares	1,080,746
Options exercisable, weighted-average exercise price	$ 1.77
Weighted- Average Remaining Contractual Life	7 years 7 months 6 days
$ 2.01-$ 4.65
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of Exercise Prices, Lower Limit	$ 2.01
Range of Exercise Prices, Upper Limit	$ 4.65
Options Outstanding, Number of Shares	1,391,205
Options Outstanding, weighted-average exercise price	$ 2.22
Options exercisable, Number of Shares	277,705
Options exercisable, weighted-average exercise price	$ 2.39
Weighted- Average Remaining Contractual Life	8 years 6 months
$ 4.66-$ 15.43
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of Exercise Prices, Lower Limit	$ 4.66
Range of Exercise Prices, Upper Limit	$ 15.43
Options Outstanding, Number of Shares	1,261,460
Options Outstanding, weighted-average exercise price	$ 9.35
Options exercisable, Number of Shares	1,261,460
Options exercisable, weighted-average exercise price	$ 9.35
Weighted- Average Remaining Contractual Life	3 years 6 months